1. Field of the Invention
The invention is directed to an improved device for supplying fuel at high pressure to an internal combustion engine.
2. Description of the Prior Art
One device of the type with which this invention is concerned, known from German Patent Disclosure DE 198 43 344 A1, is in the form of a fuel injection valve in which a bore is embodied in a valve body, and a pistonlike valve member is disposed longitudinally displaceably in the bore. The valve member has a sealing portion, with which it is guided in a guide portion of the bore, so that in this region, between the valve member and the inner wall of the bore, only an extremely small annular gap remains, which is precisely large enough to assure the longitudinal displaceability of the valve member. On the end of the guide portion of the bore toward the combustion chamber, a pressure chamber embodied by a radial enlargement of the bore adjoins the guide portion; this pressure chamber can be filled with fuel at high pressure. The pressure chamber continues, toward the combustion chamber, in the form of an annular conduit surrounding the valve member, and on the end toward the combustion chamber it is bounded by a valve sealing face that closes off the bore from the combustion chamber. The valve member, on its end toward the combustion chamber, has a valve sealing face, which cooperates with the valve seat to control at least one injection opening, so that the injection opening can be made to communicate with the pressure chamber by means of the longitudinal motion of the valve member.
On its end remote from the combustion chamber, the bore is adjoined by a leak fuel chamber, which is kept constantly at a low pressure level by a suitable leak fuel connection. Since at least during the injection a very high fuel pressure prevails in the pressure chamber, a high pressure difference prevails between the two ends of the guide portion of the bore. As a result, fuel is forced from the pressure chamber into the leak fuel chamber through the annular gap, which remains between the sealing portion of the valve member and the guide portion of the bore because of the longitudinal displaceability. Precisely in fuels of the kind used for self-igniting internal combustion engines, the fuel in this region also serves to lubricate the valve member in the bore. To improve the lubricating properties and simultaneously form the lubricant film, various types of recesses on the sealing portion of the valve member are therefore provided in the aforementioned DE 198 43 344 A1. As examples, annular grooves and indentations of circular cross section are proposed, among others, which are meant to produce a uniform lubricant film and thus lead to low wear of the valve member in the bore. Because of the high pressure difference between the two ends of the guide portion of the bore, a hydraulic transverse force occurs, if the valve member tilts, and this force presses the valve member against the inner wall of the bore. This transverse force results from a pressure drop resulting from the narrowing of the cross section in the throttle gap. In DE 198 43 344 A1, providing the annular grooves is meant to achieve stabilization of the valve member by means of a tangential pressure equalization. However, this method reduces the transverse force only at the location of the annular groove. It does not generate any pressure buildup, however, that could act as a restoring force to stabilize the valve member. As a result, excessively high wear to the valve member in the bore can occur, thus shortening the service life of the fuel injection valve or other device for supplying the engine.